Inductively loading signaling conductors



G. W. ELMEN INDUCTIVELY LOADING SIGNALING CONDUCTORS June' 1 1926..

Filed May 2, 1922 M\\\\\\ 24 fl:

Patented June 1, 1926;

UNITED. STATES PATENT OFFICE.

. GUSTAF w. EL EN, or LnONIA, NEW JERSEY, AssIeNON. TO WESTERN ELECTRIC- com IPANY, INCORPORATED, on NEW YORK, Y., A CORPORATION on NEW YORK.

INnUd'rIvELY LOAD NG Application filed May 2,

This invention relates to conductors 'for' of a cond'uctor employed for the transmis-.

sion of alternating current is to wrap the conductor spirally with a layer of wire or tape of magnetic material. This method is known in the art as continuous inductive loading as distinguished from lump loading by means of coils distributed at intervals along the conductor. Until recently iron has been considered to be the only material suitable for continuous loading. It has been discovered liowe'verthat a more suitable material may be produced in the form of an alloy of nickel and iron. When these two metals are in proper. proportions and the alloy is given a proper heat treatment a material having a very high ermeability at low magnetizing forces is. o tained. This material is known as permalloy. In its preferred form it comprises 78 70 nickel and il iron. Other properties possessedby this alloy which increase its value as loading material are small hysteresis loss and high resistivity, both conductive to increasing the efficiency of thecable by lowering the effective resistance. A

l/Vhen it was attempted to employ this material in the form of a tape for continuously loading a conductor difficulties were encountered. It was found that if the permalloy tape is first heat-treated and then cooled and applied to the conductor internal stresses areset up by the bending of the tape, causing the permeability to be very materially lowered. This difiiculty has been met in. an entirely satisfactorymanner according to this invention.

An object of this invention is to provide for the practical loading of a signaling eonductor with magnetic material which requires heat treatment and whose characteristics are subject to undesired change under applied stresses. 1

A further object of the invention is to provide a method of applying magnetic loading material to an electrical conductor in a manner to prevent the up of deleterious stresses in the magnetic mater al flaring a subsequent e t t ea me M r SIGNALING eoNnucrons.

1922. Seria11io.557,9 28.

specifically, the invention provides a method of applying loading material capable of possessing igh permeability in a. manner to avoid obtaining low and,variable values of permeability. v 1

The accompanying drawing shows, in Fig. 1, a conductor wrapped with magnetic tape and in Fig. 2 a furnace which is suitable for the heat treatment of the Wrapped conductor. g It has been found desirable to employ a tape of a thickness not exceeding 9 or 10 mils and a width of 20 to 200 mils with conductors of the orderof 100 to 200 mils in diameter. It is sometimes of advantage to use tape of only 2 or 3 mils thickness. These and other quantitative values mentioned in this specification are given by way of example only. It is to be understood that the invention is applicable under a wide range of conditions and the scope is defined only by the appended claims. 1

The ingredients of the magnetic alloy, permalloy for example, are first fused together in an induction. furnace, then molded:

into the form of a bar or rod, and may'then be worked down into the form of a wire of desired diameter. This process, as is usual, consists of successive drawings of the material until it acquires a certain degree of hardness, when it is annealed to soften it.

The drawing process is then continued until it is again necessary to anneal. This cycle is repeated until the size of wire de sired is obtained. If the loading mate-rial is to' be in the form of tape, which is the preferred form, there is substituted -for the drawing of the material during the last few cycles of operation a passingof it between rollers. may be obtained by trimming the edges.

. To give the permalloy its desired char acteristics including high permeability atsmall magnetizing forces it is necessary to heat-treat it. According to present practice this heat treatment comprises heating the. tape to a temperature of about 850 C.,' maintaining it at that temperature for afew minutes to insure a uniform temperature throughout,. then cooling slowl to a. temperature of about 600 degrees, w 'ch is just above the critical or transition temperature of the alloy, that isthe tempera ture at which the magnetic properties disappear on heating and reappear on cooling;

A uniform width of tape and finally cooling from that temperature more rapidlybut at a definite rate depend ent upon the ratio of nickel to iron in the material from the furnace when it has reached the temperature of 850 G. into. a

'l'olast of air which is controlled to secure the desired rate of cooling. The necessary cooling will always be at a rate intermediate that required for annealing and that at which such strains would be set up as to lower the permeability below the desired value.

The magnetizing forces to which the loading material upon e si naling conductor is subjected are very sma 1. They are ofthe order of 0.01 to 0.10 gauss. The permes ability of permalloy at these small forces has'been found to be from to times that of iron, that is from 3000 to 6000. The corresponding value for the best grades of iron is about 300. Thepermeability of this alloy may be reduced, however, to values of the order of 600 by the mere act of stretching the material. It would be impractical therefore to give the tape a final heat treatment before winding it upon the conductor. Such'a rocess would so lower the permeability an make'it vary so much from point to point that the loaded con- {the loading material due it is thought to ductor would be of very inferior quality.

According to the present invention the above described. difficulty is overcome by first lacin the tape upon the conductor and t en su jecting the conductor and tape to the same heat treatment. The tape is thus 'ven its desired electrical characteristics a r it is in its final shape and position.

A further difliculty was encountered in the development of this process and an additional feature of this invention is"the provision of additional steps in the'process to overcome this difiiculty. Durin'g'the cooling subs uent to the-heating, the'tempera tureof to tape than that of t e copper conductor, whici results in permanent stresses introduced in the. difference in the rates of contraction of the conductor and the loadingmaterial. The "set thus given the material mayresult in ,a greatly reducedpermeability. -According to this invention this difiiculty has been.

' overcome by-' hardening the tape material before its application to the conductor, and applying. only a moderate tension to the tape during the processof winding. The tape then appears to be rather firmly wound uponthe conductor, but in fact there is suf- I ficient spacing between the two to er'm'it 1 the above nientioneddilference 1n the mates of contraction of the conductor. and

"is lowered more qmckl .tape without producing a'set in the tape.

The value of the tension applied to the tape durin winding should be no less or' only very s ightly less than that necessary topre;

vent this deleterious effect. Nine or tenreduction in diameter or thickness during the last stage ofdrawing or rolling. For

example, a tape to have a thickness of 4 mils may have its final stage of annealing when it is 6 mils thick. I

shown as woundspirally upon the signaling conductor 11 with the edges of the adjacent turns in contact. If it were for any reason desired, the turns could be out of con- Referring to the drawing the tape 10 is tact or could overlap. The preferred form is as shown. After the winding process the heat treatment'may be effected by drawing the conductor lengthwise through the furnace shown in Fig. 2 which is maintained at a temperature of 850 degrees centigrade. This is a mufile furnace with the heating elements 20 between, the fire clay muffle 21 and the fire brick 22. Around the fire brick is a sheet iron outer wall. The iron tube 23 has a copper linin 24 of inside diameter of little over inch. This extends across thefurnace and may project beyond the furnace walls at each end.

The length of the pass through the furnace is about-'2 feet and the rate of movement of the conductor therethrough is about feet per. minute. As the tapedconductor passes through the furnace it is cooled by the air,outside which is about 20 degrees centi ade. Under the conditions and for the dimensions described this 'ves a proper rate of cooling. For ardi erent rate of withdrawal of the taped conductorfrom the furnace it may be advantageous to employ rial for oading is perma loy containing 78 of nickel and 21 75 of iron, but'the wire or tape may be of any material which requires heat-treatment and which has a characteristic subject to undesired change under applied stress.' Among the loading materials which could be used are iron nickel alloys in which the percentage varies quite widely from that herein mentioned and also alloyscontaining other ingredients in' addition to iron and, mckel-for example,

chromium, which maybe added to increase -the resistivity- The processdescfibed is also a plicable to the case where several layerso wire or .tape are used, the adjacent layers of wire or tape being applied to the conductor in" either the same or in opposite directions. It is sometimes advisable to use two or more layers of wire or tape, rather than one layer maintaining for a considerable time a' tem perature slightly above the transition point;

greater. thickness, rent losses.

In a broad aspect the invention'is not limited to the use of wire or tape. The layer of loading material may be applied in some other manner, butit must be in such a way that strains will not be set up in it during cooling of the loaded conductor after the final a plication of heat.

It is wit nn the scope of the invention to operate the furnace in which the loaded conductor is heated at a temperature varying considerably from that mentioned above.

'It is necessary that the heating above the magnetic transition temperature be of a nature to render the structure of the alloy uniform throughout. This may be done by but the process will be materially hastened if a very. much higher temperature is maintained', and no harm will result. In order to maintain uniform structure throughout the material; it is'also highly desirable to keep the conductor straight both while being heated and cooled. pletely understood what action takes place during the heating process, but there. is

evidence tosupport the view that a recrystallization of portions of the alloy, in which crystals were broken down by "previous working of the material, takes place. I

There is mentioned above the difference in rates of contraction of the loading tape and thecopper conductor during the cooling stage of the heat treatment as a cause of low permeability of the heat treated loaded conductor. It may be that the contactof the 'hot loading material and conductor under pressure resulting from thedifierence'in rates of'c'o'ntrac-tionof the two,

' materials causes them to adhere orweld at numerous points so that further cooling. results in strains set up between these-points.

i There is evidence to support this view. It

may be too that the hardness of the magnetic material is. per se of advantage in obtaining maximum benefit from-the heat treatment as well as being a practical way of obtaining the desired looseness. Other explanations for the observed efiect have been made, but, whatever-the cause, the effect is substantially overcome or fievented by. this invention.

For a more detailed account of the properties of the loading material described heresee a lication of G. W- Elmen Serial 1n No, 453,8 ,filed May 31, 1921. A. complete to reduce the-eddy cur- It is not comdisclosure of the advantages of this material as a loading material for submarine telegraph cables-is made in the application of E. Buckley, Serial No.- 492,72'5, filed Aunnst 16 1921. .4

That isclaimed is:

Y 1. The method of loading a signaling conductor with magnetic alloythe permeability of which varies materially when the alloy is strained, which comprises forming a layer of said alloy about the conductor :so that the space Within the loading layer is not completely occupied by. the material of the conductor, and subjecting the loaded conductor to heat treatment, the layer being so formed that the conductor has room for ex- ..pansion during the heat treatment.

2. The method'of producing a signaling conductor loaded with magnetic material which requires heat treatment-to give it high permeability and the permeability of whichis sensitive to strains, which comprises forming a layer of said material about the conductor, so that the space within the layer is not completely occupied by the material of the conductor and. subjecting the loaded conductor to the said'heat treatment by passin'git through a furnace and then through a cooling medium without bringing the conductor forcibly in contact with the inner surface of the loading layer.

3. The method of loading a signaling conductor the wire or tape of a material which requires heat treatment for maximum permeability, which comprises winding the wire or tape spirally upon the conductor before the final heat treatment and in such manner thatthe layer of loading material when cold will fit the conductor closely enough to prevent material slipping upon the conductor during the handling of the latter but not so tightly that the conductor during cooling after the final application of heat will interfere with contraction of theloading material when the cooling is ata proper rate to give high permeability, heating the wrapped con-' I ductor above the critical temperature of the the space within the layer is not completely I occupied by the material of the conductor, passing the loaded conductor through a turnace' and a cooling medium in succession.

and maintaining in a substantially'straight'.

condition that portion of the conductorwhich is being heated and cooled.

5. The method of loading a signaling com ductor withumagnetic material in-the form of a wire or tape which comprises wrap-v con ctor. under a moderate tension. heating the wound conductor above the critical temperature of the magnetic material and subsequently cooling iteat a ratenecessary to give said material highpermeability when cold, said tension being great enough to cause the wire or tape to lie in place-while the conductor is handled but not great enough to cause such a close fit that the conductor will be brought forcibly in contact with the tape during said cooling process.

6. The method of loading a signaling con-'v ductor with magnetic material in the form of a wire or tape which comprises regulating the hardness of the wire or tape, wraptor, but not so great that the conductor, when undergoing said coolingprooess will set up a tension in the tape.-

7. The method of loading a signaling con ductor with magnetic material in the form of wire or tape, which comprises wrapping "the-wire or tape spirally" aroundthe conductor under-a moderate-tension, heating" the wound conductor well above the critical 7 temperature oithe'magnetic material, cooling it slowlyto a point just above the critiv cal temperature and completing the cooling more rapidly at a predetermined rate whereby said material is given high permeability;

when cold, said tension being great enough to prevent the tape from subsequentlyover lapping 'or materially slipping during han- 45 dling of the conductor but not great enough 1 to cause such a close fit that the conductor Wlll set up a ten'sion in the magnetic material during said cooling process.

s. Thegnethod ofloading a signaling an.

ductori vmagnetic material which requires h "treatment for maximumpermeabilityj' iph comprises surrounding the conductor with a layer of the magnetic material fitting the conductor loosely enough at least to prevent the conductor during the cooling after the. final application of heat from interfering with contract-ion of the loading material when the cooling is at a proper. rate to give high permeability, heating the loaded conductor above the magnetic transition temperature of the loadingmaterial, and cooling it atsaidrate.

1 9. The combination with a copper 'conduc tor of a layer of'magnetic material thereabout WhlChz-iS capable of having developed therein high permeability magnetizing ping the wire or tape spirally about the insane? forces encountered in signaling, but which.

the space inside said layer of loading mate rial not being entirely taken up by said conductor, whereby the conductor has room for expansion during the heat treatment.

10. The combination with a copper conductor of a layer ofgnagnetic material thereabout which is capable of having developed there-in high permeability at magnetizing forces encountered in signaling, but which has to be heat treated after being applied to the conductor to obtain high permeability, the loading layer fitting the conductor loosely, whereby the conductor has room for expansion during the heat tr 11. The combination with a signaling conductor, of a layer of hardened wire or tape laid spirally thereon to increase the inductance, said wire ortape being of an alloy which is capable of having high permeability developed therein by heat treatment.

12. The combination with a signaling conductor, of a non-adherent layer of hard- .ened alloy formed over said conductor increase the inductance, said alloy consisting chiefly of nickel and iron.

. l.-=.. l3. 'ilhe combination with a signaling conductor, of a layer of hardened wire or tape laid spirally thereon to increase the in ductance, said wire ,or tape being of an alloy consisting chiefly of? nickel and iron.

14:. The combination with a conductor, of a layer of magnetic material thereabout the permeability of which is more sensitive to strain than that of iron and which is capable of having developed therein high permeability at magnetizing forces encountered in signaling, but which has to be heat treated after being applied to the conductor to'obtain high permeability, the inner Surface of said loading material being retained out of forcible contact with the outer surface of said conductor in such manner as to==-relieve or prevent strains which would materially lower the permeability.

15. The method of continuously loading a signaling conductor with magnetic material capable of having higher permeability than iron developed therein at magnetizing forces encountered in signaling, which comprises hardening the material, surrounding the conductor with a layer of the material in hardened form, heating the loaded conductor to a temperature below the melting point of the conductor and cooling it.

16. The method of continuously loading a copper signaling conductor with magnetic material consistin chiefly of nickel and iron, which comprises hardening the magnetic material, surrounding thefconductor with a layer of the material in hardened form, heating the loaded, conductor. to. a temperature below the, melting point pf the conductor and cooling it, a portion of the cooling being at a rate greater than an annealing rate and which Will develop higher permeability in the loading material than an annealing rate.

17. The method of continuously loading a signaling conductor with magnetic material which comprises forming the material into a Wire, alternately annealing and reducing the diameter of the Wire by drawing, subsequently forming the Wire into a tape and trimming the edges toproduce a tape of uniform Width, the final stage before trimming being one of mechanical working to harden the tape, and Winding the tape spirally upon the signaling conductor, with slight spacing therebetween.

18. The method of preparing magnetic material for inductive loading which com prises alternately annealing and reducing the thickness of the material by mechanical working, the final stage being one of mechanical working suflicient to reduce the thickness by at least one-half the thickness of the finished material.

19. The method of preparing nickel-iron alloy for inductive loading which comprises alternately annealing and reducing the thickness of the material by mechanical Working the final stage being one of mechanical Working suflicient to reduce the thickness by atleast one-half the thickness of the finished material.

20. The method of continuously loading a signaling conductor with nickel-iron alloy which comprises alternately annealing and reducing the thickness of the alloy by mechanical working, the final stage being one of mechanical working snificient to reduce the thickness by at least one-half the thickness of the finished -material, subsequently applying the alloy to a signaling conductor and heat treating the alloy on the conductor In witness whereof, I hereunto subscribe my name this 26th day of April A. D., 1922..

'GUSTAF WV. ELMEN. 

